1. Field of the Invention
The present invention relates to a load sharing device and a parallel power supply therewith, and more particularly, to a load sharing device that can more simply implement a LS control constitution and obtain more improved load sharing property, while maintaining output voltage of each of parallel power supply modules within a control range, and a parallel power supply therewith.
2. Description of the Related Art
Generally, a medium-large capacity power device widely uses a plurality of power supply modules connected in parallel, and FIG. 1 is a diagram showing a specific example of the power supply including such parallel power supply modules.
Referring to FIG. 1, the power supply is configured of an AC-DC front end converter, a point-of-load (POL) converter, etc. The AC-DC front end converter converts AC voltage into DC bus voltage, and it supplies power to each load through the POL converter. In such a power supply, the AC-DC convert and the POL converter widely use a parallel module shape due to the following reasons:
(1) Thermal management and reliability: In a parallel structure, each power module operates only a portion of the entire power to reduce the loss power of each module, such that the thermal management is facilitated and the reliability of a system is enhanced.
(2) Redundancy: In a system requiring a high reliability, a redundant structure of N+1, as shown in FIG. 1, is used. In other words, one module is added into n minimum parallel modules to be driven, the system is operated using the n modules when any one module is out of order, such that the system can be maintained and fixed without affecting the load and the entire system.
(3) Modularity: A parallel structure facilitates a modularity design of a system. In other words, only the number of module can be controlled and applied according to a capacity of the system using one designed module.
Based on the above reasons, it is preferable to implement a power supply having a parallel constitution rather than a unitary power supply, and the power supply having such a parallel constitution will be described with reference to FIG. 2.
FIG. 2 is a diagram explaining a structure where two independent power modules are driven in parallel, wherein (a) is a equivalent circuit view showing a structure where two parallel power modules are driven, and (b) is a graph showing current distribution property of the equivalent circuit shown in (a).
Referring to FIG. 2, each of power supply modules 101 and 102 can implement an equivalent circuit with output voltages Vth1 and Vth2 and output resistors Zoc1 and Zoc2, in unloading. If the output voltages Vth1 and Vth2, the output resistors Zoc1 and Zoc2, and parasitic resistors Zc1 and Zc2 of the two modules 101 and 102 are ideally the same, output currents Io1 and Io2 is evenly distributed to the two modules 101 and 102 to be flowed.
However, since there is actually a deviation between the two modules 101 and 102, as shown in FIG. 2(b), the current distribution property is determined in voltage VoL of a junction node of the two modules. In other words, as the deviation of the voltage Vth1 and Vth2 and the resistors Zoc1+Zc1 and Zoc2+Zc2 is larger, the load sharing (LS) property, which is the current distribution property, is deteriorated.
Therefore, in the case of a 12V power device for server, although an error of initial output voltage between the two modules 101 and 102 is only several tens of mV, one module bears all load current. For this reason, in the parallel power supply, there is a demand for an additional LS control for enhancing the reliability and improving the LS property.
Reviewing one example of such a LS control in the related art, it may be divided largely into a LS control in a drop current sharing mode (hereinafter, referred to as ‘Droop mode’) and a LS control in an active current sharing mode (hereinafter, referred to as ‘Active mode’).
However, with such technologies in the related art, problems arise in that LS errors are large and output voltages of the respective power supply modules cannot escape from a control range (the LS control in the Droop mode), and a control is relatively complicated and the change in the output voltages due to the LS control may become large when a deviation of individual modules is large (the LS control in the Active mode). Such problems act as a limitation in accomplishing the more improved LS property through a simple implementation, such that they are not preferable LS control technologies.
In order to overcome such problems, there is an acute demand for a load sharing device that can more simply implement a LS control constitution and obtain more improved LS property, while maintaining the output voltages of the respective parallel power supply modules within a control range, and a parallel power supply therewith.